JP2699376B2 - Resin temperature control device for injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resin temperature control device of an injection molding machine that controls the temperature of a molten resin flowing into a cavitation in injection molding by rotating a screw.

(Prior Art) In injection molding, a synthetic resin is changed from a pellet to a molten resin by an electrically heated barrel at the tip of an injection cylinder and shear heat generated by a screw. In order to control the temperature of the molten resin, there is disclosed, for example, JP-A-61-2558.
No. 25, JP-A-62-132627 and JP-A-60-15
It is proposed to provide a temperature sensor in the cavity or injection cylinder to measure the temperature of the molten resin, and to operate the injection holding pressure switching device, heat pump, etc. with this measurement output signal to control the temperature. Have been. FIG. 2 shows a barrel 2 and a mold cavity 3 of an injection molding machine 1.
The output of the temperature sensor 4 provided therein is calculated (calculation circuit 5), and the heater 7 provided in the injection cylinder 6 is controlled (control circuit 8).
Is what you do. These devices measure the temperature for each injection molding and control the state of the molten resin. As another heat source, the barrel supplies much less heat than the heat generated by the shear heat of the screw, and cannot change the heat instantaneously. Since the amount of heat can be changed depending on the internal pressure of the resin (back pressure) and the number of revolutions of the screw at the time of conversion, it is effective as a control object. However, when the pellets in the hopper are supplied into the injection cylinder for the purpose of measuring the raw material, the rotation speed of the screw may be changed in relation to the load (the amount of the pellets) (Japanese Patent Laid-Open No. 62-132624). Also,
The screw rotation speed was not changed for the purpose of changing the heat quantity.

Actually, the number of rotations of the screw becomes a value determined by the condition setting value and the material characteristics, and the temperature of the molten resin can be kept almost constant. That is, the temperature is slightly lowered before and after the operation at the time of injection, but the control is performed so that molding can be performed with the average value with the set temperature.

(Problem to be solved by the invention) Actually, when injection is performed from an injection molding machine into a cavity,
The molten resin that comes into contact with the mold surface layer is first solidified to form the surface of the product (0.1 to 0.2 m / m thick). However, when the resin temperature is low, the solidified product surface thickness increases and the resin flow path increases. As the internal pressure is increased and the internal pressure is increased, mold distortion is gradually increased, and burrs are generated in the runner portion and the PL (parting line) near the gate, thereby causing defects such as mold damage. Therefore, it was necessary to increase the mold strength.

In addition, in a part where the cavity is difficult to cool due to the product shape, it is desirable that the synthetic resin filling the cavity is a low-temperature molten resin. Increase. When filling is completed, it is necessary to maintain the pressure by replenishing the synthetic resin in order to prevent shrinkage due to cooling and hardening shrinkage (underfilling). Becomes impossible. Therefore, a large gate is required so as to slow down the gate seal, and post-processing of the gate is required. In such a case, it is desirable to flow the molten resin at an optimum temperature into a predetermined location in the cavity. However, in a system in which a temperature sensor or the like is attached to a predetermined location and feedback is applied to the heating means on the injection cylinder side to control the real-time, And cannot be filled with a molten resin at a desired temperature. For example, conventional technology (Japanese Patent Application Laid-Open No. 60-157823)
When the temperature sensor is installed in various places as shown in the above, even if the output signal of the temperature sensor is calculated and the command to set the predetermined temperature is added to the heating means, the temperature detected by the temperature sensor and the filling amount of the molten resin (filling position) Is indeterminate, the molten resin at an inappropriate temperature flows in.
That is, if the filling position is not accurate with respect to the temperature, the feedback control becomes unstable.

Here, the filling amount (filling position) can be known by measuring the advance distance of the screw of the injection cylinder, and the rotation of the screw can change the temperature of the resin, and has a correlation with each other.

The present invention provides an in-line screw type injection molding machine that controls the temperature of a molten resin in a single injection step for injection filling into a mold cavity, and reproduces continuously in each injection step. It is an object of the present invention to provide a resin temperature control device of an injection molding machine capable of performing the following.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a means for detecting a position of a screw when a molten resin is injected and filled into a mold cavity of an injection molding machine, and a mold cavity. A setting device having setting data of the position and the number of rotations of the screw corresponding to the temperature of the molten resin filled in the screw, a screw position detected by means for detecting the position of the screw, and a screw position of the setting data Is calculated, and based on the result of the comparison, the rotational speed of the screw corresponding to the temperature is determined in order to change the molten resin in a single step of injection filling into the mold cavity to a desired temperature. A comparison operation circuit and a rotation speed of a hydraulic motor for rotating the screw are controlled based on the rotation speed of the screw determined by the comparison operation circuit. Controlling means.

The setting data for the temperature of the molten resin injected and filled into the cavity at the time of filling is obtained as follows. First, a temperature sensor is attached to the injection noise, the correlation coefficient between the screw rotation speed and the resin temperature, and the contribution coefficient to the resin temperature due to the change rate of the screw rotation speed during the same plasticization are obtained in advance. The rotational speed of the hydraulic motor is controlled so that the rotational speed is set in accordance with the position of the screw, and the molten resin injected and filled into the cavity is changed to a desired temperature.

(Operation) In the case of using the apparatus of the present invention, the rotational speed corresponding to the position of the screw is adjusted so that the molten resin injected and filled into the mold cavity has a desired temperature by setting data of the setting device. decide. Under these conditions, injection filling of the molten resin into the mold cavity is started. The position of the screw 15 at this time is detected by the detector 18. After that, the position of the screw 15 at the time of injection filling is compared with the position of the screw of the setting data possessed by the setting device, and the rotational speed of the hydraulic motor is controlled so as to correspond to the position of the screw. The molten resin is changed to a desired temperature in one step of injection filling. That is, by changing the rotation speed of the screw according to its position, the shear heat generated by the screw is changed,
The temperature of the molten resin is changed to inject and fill the mold cavity.

(Example) An example of the present invention will be described with reference to FIG. In the figure, an injection device 11 is provided with a heating cylinder 14 having a hopper 12 for supplying a raw material and a nozzle 13 for injecting a molten resin into a mold cavity, a screw 15 disposed in the heating cylinder 14, and a forward drive of the screw 15. And a hydraulic motor 17 that rotates. The hydraulic motor 17 is connected to a hydraulic source 21 via an oil amount adjusting valve 22, and the oil amount from the hydraulic source 21 is adjusted by operating the oil amount adjusting valve 22. That is, by operating the hydraulic pressure control valve 22, the rotation speed of the screw 15 can be changed.

The injection cylinder 16 is provided with a detector 18, which detects the position of the screw 15 disposed in the heating cylinder 14. The detector 18 is connected to a comparison operation circuit 19 including a screw position comparison circuit 19a and a screw rotation speed setting value switching circuit 19b. In the comparison operation circuit 19, a screw position comparison circuit 19a connected to the detector 18 is provided at a preceding stage, and a screw rotation speed setting value switching circuit 19b is provided at a subsequent stage. The screw rotation speed setting value switching circuit 19b of the comparison operation circuit 19 is connected to the oil amount adjustment circuit 23. The oil amount adjustment circuit 23 operates the oil amount adjustment valve 22 in a controllable manner.

A plurality of screw position setting devices 20 are provided in the screw position comparison circuit 19a and the screw rotation speed setting value switching circuit 19b.
a, 20b... and screw rotation number setting devices 20c, 21d. That is, the setting unit 20 including a plurality of screw position setting units 20a, 20b... And screw rotation speed setting units 20c, 20d.

Although not shown, a temperature sensor is attached to the nozzle 13. Then, based on the output result of the temperature sensor attached to the nozzle 13, the correlation coefficient between the screw rotation speed and the resin temperature, and the contribution coefficient to the resin temperature due to the change rate of the screw rotation speed during the same plasticization are calculated. It is required in advance. Screw rotation speed setting devices 20c, 20d…
.. Correspond to the position of the screw 15 so that the temperature of the molten resin injected and filled from the nozzle 13 is changed to a desired temperature depending on the position of the screw 15 (the amount of the molten resin charged into the mold cavity). The rotation number (setting data) of the screw 15 is stored. The screw position setting devices 20a, 20b... Store setting data of the position of the screw 15. A large number of setting data are set so that they can be appropriately handled according to the type of the mold cavity used.

 Next, the operation will be described.

In the present invention, when the molten resin is injected and filled into the mold cavity through the nozzle 13, the molten resin can be brought to a desired temperature by adjusting the rotation of the screw (shear heat generation). In the embodiment, at the initial stage of injection filling of the molten resin into the mold cavity, the screw rotation speed is set to a predetermined (high) rotation, and the injection filling is performed while changing the screw rotation speed in accordance with the setting data so as to lower the screw rotation speed. It will be described in some cases.

First, when the comparison operation circuit 19 is operated, the set value of the rotation speed of the screw 15 stored in the first stage screw speed setting device 20c is read, and a signal is sent to the oil amount adjustment circuit 23. The oil amount adjusting circuit 23 receives this signal and supplies a predetermined amount of oil from the hydraulic source 21 to the hydraulic motor 17 to rotate the screw 15. Thus, the pellets supplied from the hopper 12 are compressed and sheared and melted in the course of being sent toward the tip of the screw 15 in the heating cylinder 14. Then, due to the pressure of the resin sent to the tip of the screw 15, the screw 15 retreats so as to accumulate one shot of the molten resin at the tip of the heating cylinder 14. At this time, when a weighing start signal is output and the screw 15 is retracted to a predetermined position, an injection cylinder is used to inject the molten resin into the mold cavity.
16 is driven to advance the screw 15.

The position of the screw 15 is detected by a detector 18 provided on the injection cylinder 16 and input to a screw position comparison circuit 19a. The screw position comparison circuit 19a
The position of the screw 15 detected by the above is compared with the setting data of the first-stage screw position setting device 20a, and a signal is output to the screw rotation speed setting value switching circuit 19b when both values become the same value. . The screw rotation speed setting value switching circuit 19b is a second stage screw rotation speed setting device based on the signal input from the screw position comparison circuit 19a.
The rotation number of the screw 15 corresponding to the position of the screw 15 stored in 20d is read and output to the oil amount adjustment circuit 23. The oil amount adjusting circuit 23 is operated by the oil amount adjusting valve according to this signal.
Hydraulic motor 17 that adjusts 22 and rotates screw 15
Change the rotation of. That is, in the case of this embodiment, the rotational speed of the hydraulic motor 17 that drives the screw 15 by rotating the oil amount adjusting valve 22 is reduced. As a result, the temperature of the molten resin changes so as to be lower than the initial temperature during the injection and filling into the mold cavity.

Furthermore, the position of the screw 15 is detected, the rotation speed of the screw is changed according to the set data, and the change of the temperature of the molten resin is repeated. The temperature of the molten resin is selected to be an optimum value according to the mold cavity to be injected and filled, and the number of revolutions of the screw for generating heat by shearing the pellets is controlled so as to be at the selected temperature.

(Effect of the Invention) Since the present invention is configured as described above, the rotation speed is changed according to the position of the screw according to the position of the screw according to the setting data during the filling into the cavity during the injection molding, and the temperature of the molten resin is changed. The rotation of the screw is controlled by setting data so that the temperature of the molten resin injected and filled into the mold cavity is optimized according to the state of the injection filling process, and the temperature of the molten resin flowing into the mold cavity is controlled. Can be changed. In other words, when the mold is first injected at a high temperature during injection filling into the mold cavity, the flowability of the synthetic resin is improved, so that molding can be performed at a low pressure, and therefore, the mold strength can be reduced. Can be saved.

Near the completion of injection filling, by lowering the resin temperature,
Cooling and curing time can be shortened. In addition, since the pressure can be easily maintained after the filling is completed, the gate can be made smaller and the number of gates can be reduced.Therefore, the number of weld lines is reduced, the number of gates is reduced, and the number of steps required for post-processing is reduced. This has the effect of increasing the product value. Further, since the filling efficiency is good, when the number of gates is not changed, the processing time of one process is shortened, and the productivity is improved. Further, there are effects such as reduction of design constraints and reduction of design change.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the gist of the present invention, and FIG. 2 is a schematic diagram of a conventional resin temperature control device. 11: Injection molding machine, 15: Screw 17: Hydraulic motor, 18: Detector 19: Comparison operation circuit, 20: Setting device 22: Oil amount control valve, 23: Oil amount adjustment circuit

Claims (1)

(57) [Claims] 1. A means for detecting a position of a screw when a molten resin is injected and filled into a mold cavity of an injection molding machine, and a position of the screw corresponding to a temperature of the molten resin filled in the mold cavity. And a setting device having setting data of the number of rotations, a screw position detected by the means for detecting the position of the screw and a screw position of the setting data are compared, and a mold cavity is formed based on the comparison result. A comparison operation circuit for determining the number of rotations of the screw corresponding to the temperature in order to change the molten resin to a desired temperature in one step of injecting and filling the inside, and the rotation of the screw determined by the comparison operation circuit Means for controlling the number of rotations of a hydraulic motor for rotationally driving the screw based on the number of rotations. Fat temperature control device.